While some janitors struggle to get by, others are climbing into the middle class. Behind the new battle over America's low-wage workers

It's 9 P.M., and Craig Jones has just finished dumping 400 trash cans' worth of garbage into the Cincinnati Textile Building's basement compactor. The weighty refuse he carries each night hardly fazes Jones after five years on the job, but the grime he has to scrub off dirty wastebaskets still gets to him a little. "Wiping spit is a tough thing to get used to," he says. Jones, 27, earns $6.50 an hour without benefits, vacation time or sick days. His employer, Professional Maintenance, a cleaning contractor, usually schedules him for just four hours a night, five nights a week, so Jones'...